jpvantassel/hvsrpy: v0.5.1

In this release

• 🐛 Fix bug related to f0_mc when using upper and lower frequency limits.
• 💥 Remove reference to WindowedTimeSeries and FourierTransformSuite in compliance with recent sigpropy release.
• 🔨 Refactor methods to remove superfluous if statements after aforementioned removals.
• ✅ Improve testtools.py to be more performant and easier to understand.
• ✅ Increase unit test coverage.
• 📚 Various updates to API documentation.